1. Field of the Invention
The present invention relates in general to a worm gear unit that includes mutually meshed worm shaft and worm wheel and a method of producing the same, and more particularly a Niemann type worm gear unit and a method of producing the same. The Niemann type worm gear unit comprises a Niemann type worm shaft and a Niemann type worm wheel.
2. Description of the Related Art
Various worm gear units have been hitherto proposed and put into practical use particularly in the field of motor vehicles. The worm gear unit is sometimes called just “worm gear”.
One of them is disclosed in Japanese Laid-open Utility Model Application (Jikkaihei) 4-56250. The worm gear unit shown in the publication is of a Niemann type that comprises a Niemann type worm shaft and a Niemann type worm wheel which are operatively engaged or meshed when in use. The worm shaft and worm wheel of such type have arc-shaped continuous ribs (or helical tooth ridge) and arc-shaped teeth respectively. Due to the nature of such Niemann type, the continuous ribs and teeth of the worm gear unit have a larger face width, and thus, the continuous ribs and teeth of the Niemann type worm gear unit can have an increased mechanical strength.